The art has long recognized the need for a reliable and accurate system for measuring and displaying the location of a vehicle. Such a system would be of obvious and great value to the military, to police departments, to taxi and other transit services, and to many fleet owners and an inexpensive system would be of great value to the general driving public. A number of systems have been proposed which can be categorized as being proximity, triangulation or dead-reckoning systems. Proximity systems require a network of route markers, e.g., "signpost" transmitters, require a large amount of community commitment and support and cannot be readily unilaterally undertaken by private firms or individuals. Triangulation systems also require community cooperation for locating and maintaining broadcasting stations, and further require sophisticated on-board telemetering equipment.
Dead-reckoning systems have the advantage of being self-generating but also have drawbacks. Errors which occur with a dead-reckoning system can accumulate if the system is not periodically updated and prior dead-reckoning systems based on the use of compasses have usually preferred the use of expensive and intricate gyrocompasses so as to limit the magnitude of errors. Other dead-reckoning systems have been proposed in which differential wheel displacement is used to calculate heading information, but side winds can affect the apparent direction of travel, a problem not suffered by compasses. On balance, the art has not encouraged the use of dead-reckoning systems.
The present invention provides a dead-reckoning system which is reliable and accurate and yet inexpensive. Specifically, an odograph is provided which integrates distance-traveled signals with heading signals to generate location information which can be displayed or otherwise used to pinpoint the location of a vehicle. In one embodiment of the invention, the accuracy of distance-traveled information is made more accurate by probabilistic proportioning of the signals to obtain a correspondence of indicated distance to actual distance. In another embodiment, a unique heading indicator assembly is provided which incorporates a spherical magnetic compass element and electro-optical sensing components which cooperate therewith to generate accurate and reliable heading information, yet in a manner that requires only relatively inexpensive components, permitting utilization of the system by the general public.
More specifically, a magnetic spherical compass element is provided with reflective markings, and means are provided for directing light beams onto the spherical surface. The light beams pass through lenses which rotate along vertically directed paths respective the surface of the compass element. The reflective markings are proportional in length, at least approximately, to the positive cosine of azimuthal angle from a predetermined heading such as North, so that the extent of coincidence of the light beam therewith is indicative of departure from such predetermined heading. By providing for lenses rotating in quadrantal array respective the compass element surface, with appropriate electro-optical sensors, four subsystems are obtained, one each for East, West, North and South.
In particular embodiments, the light beams are formed from a lamp filament light source and are reflected from ellipsoidal mirrors onto the spherical surface, coincident beams being reflected back via the ellipsoidal mirrors and via appropriately dipsosed beam splitting mirrors, onto optical sensors.
Prior art of interest respective the present development includes:
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